In clinical psychology, voyeurism is the sexual interest in or practice of spying on people engaged in intimate behaviors, such as undressing, sexual activity, or other activity usually considered to be of a private nature. In popular imagination the term is used in a more general sense to refer to someone who habitually observes others without their knowledge, with no necessary implication of sexual interest.

Voyeurism (from the French voyeur, “one who looks”) can take several forms, but its principal characteristic is that the voyeur does not normally relate directly with the subject of their interest, who is often unaware of being observed. The voyeur may observe the subject from a distance, or use stealth to observe the subject with the use of peep-holes, two-way mirrors, hidden cameras, secret photography and other devices and strategies.